The invention relates generally to electronic circuits and more particularly to a signal-controlled oscillator and a method for generating an oscillator-output signal having a frequency that lies within a stable frequency range.
To save time and resources, integrated-circuit (IC) manufacturers often use similarly or identically designed subcircuits in different applications, such as in different versions of an IC. For example, a manufacturer may include similarly designed oscillators in all versions of a microprocessor. Or, the manufacturer may use similarly designed memory-cores in all versions of a memory chip. Because the time and costs associated with creating, testing, and troubleshooting a single circuit design are significantly less than those associated with creating, testing, and troubleshooting multiple circuit designs, the manufacturer saves significant engineering time and costs by using similarly designed subcircuits in multiple versions of an IC.
Unfortunately, similarly or identically designed subcircuits may not operate. properly in all applications. For example, suppose that first and second versions of an IC operate at different internal clock frequencies and the manufacturer wants to use similarly designed oscillators in both IC versions. Therefore, each similarly designed oscillator must be capable of generating two different frequencies; a first frequency for the first IC version and a second frequency for the second IC version. But unfortunately, such oscillators are often unable to generate one or both of the first and second frequencies if operating conditions, such as temperature and supply voltage, or component characteristics, such as the thicknesses of transistor gate dielectrics, vary from ideal levels and the difference between the first and second frequencies is large. That is, under ideal conditions, such an oscillator can generate a signal within a frequency range that includes both the first and second frequencies. But if operating conditions or component characteristics are not ideal, then the frequency range of the oscillator signal may shift or shrink such that it includes none or only one of the first and second frequencies.
In one aspect of the invention, an oscillator includes an oscillator circuit that receives a control signal having a signal level. The oscillator circuit generates an oscillator signal having a frequency that is proportional to the signal level and that is within a frequency range. A compensation circuit stabilizes the oscillator circuit such that the frequency range includes first and second predetermined frequencies.
Thus, such an oscillator can be used to generate an oscillator signal having a first frequency in one application and having a second frequency in another application. The compensation circuit stabilizes the frequency range of the oscillator signal so that it includes the first and second frequencies over broad ranges of operating conditions such as temperature and supply voltage and over broad ranges of component characteristics such as gate dielectric thickness.